The present invention relates to an optical recording medium on which information about recording tracks is recorded in the form of a bit pattern, an optical recording medium substrate for use in the optical recording medium, a method of manufacturing a master disk for use in manufacturing the optical recording medium, and a method of accessing tracks provided on the optical recording medium.
In recent years, disk recording/reproducing systems, each being small and having a large storage capacity and a high access speed, have come into use in increasing numbers. In these systems that optically record and reproduce data, magneto-optical disk system is reliable and can repeatedly record data on the recording medium and erase data therefrom. The magneto-optical disk system is therefore widely used.
Used as a recording medium in the magneto-optical disk system is a magneto-optical disk. The magneto-optical disk in common use has either concentric grooves or a spiral groove in the signal recording surface, for guiding the recording/reproducing laser beam along the recording tracks. The recording tracks are formed along the either concentric grooves or the spiral groove.
A magneto-optical disk of this type has been proposed, in which the recording tracks are divided into sectors having an appropriate length so that the tracks may be easily recorded and accessed. Management information, such as physical addresses, is recorded in the sectors so that data may be processed in units of sectors. In the magneto-optical disk of this type, the recording area is divided into several zones in most cases, for which different basic clock signals are allocated, and each track is divided into tens to hundreds of sectors.
In this magneto-optical disk, the management information for each sector is written, in the form of emboss pits, in a region called xe2x80x9clandxe2x80x9d provided between the adjacent grooves, so that the disk may be easily produced in great quantities.
In recent years, it has been proposed that the track pitch be decreased to enhance the recording density on the surface of the magneto-optical disk. This is because the amount of information processed in the magneto-optical disk system has increased.
If, however, the track pitch is decreased on the magneto-optical disk of the type mentioned above, however, it will be difficult to form pits for the management information between the adjacent grooves. In the process of manufacturing the master disk of the magneto-optical disk of this type, two laser beams spaced apart by half the track pitch are applied to the resist film formed on a glass substrate. A latent image for the pits and another latent image for the grooves are thereby formed on the resist film. If the tack pitch is decreased, the two laser beam will interfere with each other, inevitably irradiating the region between each pit and an adjacent groove. Consequently, desirable latent images may not be formed in some cases. Magneto-optical disks made by the use of such a master disk have but a low reproducing modulation factor of pits, and appropriate signals cannot be reproduced from these magneto-optical disks.
In order to eliminate this drawback, a system has been proposed in which no grooves are made in any region where pits for the management information are to be formed. (Hereinafter, the system will be referred to as xe2x80x9cdiscontinuous groove type.xe2x80x9d)
With a magneto-optical disk of the discontinuous groove type, however, it is difficult to access the desired track at high speed. That is, on the magneto-optical disk of the discontinuous groove type, the region where the pits representing the management information are formed has a so-called mirror part that has neither pits nor grooves. When the light spot of the reading laser beam moves across a track over the mirror part in the seek operation to access the desired track, no signal is generated to indicate that the light spot has crossed over a track. As a consequence, the number of tracks the light spot has crossed may not be correctly counted in some cases.
The present invention has been made in consideration of the existing technology described above. The object of the invention is to provide an optical recording medium which can record data at high density and on which a target track can be accessed at high speed, an optical recording medium substrate for use in this optical recording medium, a method of manufacturing a master disk for use in manufacturing the optical recording medium, and a method of accessing tracks provided on the optical recording medium.
An optical recording medium according to the invention has recording tracks formed along either concentric grooves or a spiral groove. Information is recorded on the lands provided between the grooves. The recording area has regions where no grooves are made. Each non-groove region has a part that corresponds to a land. In this part of each region, a pit pattern representing information about the recording track is formed. The optical recording medium is characterized in that a detection pattern is provided on each region where no groove are made, in order to optically detect that the light spot of a reading laser beam has moved across the recording track.
In the course of accessing a track provided on this optical recording medium, the reading laser beam is applied to the detection pattern, generating a signal, as the light spot of the reading laser beam moves across the region where no grooves are made. The signal is used to count tracks, making it possible to access the track at a desired high speed.
With the optical recording medium it is desired that each detection pattern be provided in the form of a U-groove along the recording track, integrated with the pit pattern. If the detection pattern is a U-groove, provided integral with the pit pattern, it will be formed with ease.
An optical recording medium substrate according to the invention is designed for use in an optical recording medium which has recording tracks formed along either concentric grooves or a spiral groove. Information is recorded on the lands provided between the grooves. The recording area has regions where no grooves are made. Each non-groove region has a part that corresponds to a land. In this part of each region, a pit pattern representing information about the recording track is formed. The optical recording medium substrate is characterized in that a detection pattern is provided at a part corresponding to each region where no grooves are made, in order to optically detect that the light spot of a reading laser beam has moved across the recording track.
In the course of accessing a track provided on a optical recording medium using the optical recording medium substrate, the reading laser beam is applied to the detection pattern, generating a signal, as the light spot of the reading laser beam moves across the region where no grooves are made. The signal is used to count tracks, making it possible to access the track at a high speed which is desired.
With the optical recording medium substrate it is desired that each detection pattern be provided in the form of a U-groove along the recording track, integrated with the pits that form the pit pattern. If the detection pattern is a U-groove, provided integral with the pits forming the pit pattern, it will be formed with ease.
According to the invention there is provided a method of manufacturing a master disk for use in manufacturing an optical recording medium that has recording tracks formed along either concentric grooves or a spiral groove. Information is recorded on the lands provided between the grooves. The recording area of the medium has regions where no grooves are made. Each non-groove region has a part corresponding to a land. In this part of each region, a pit pattern representing information about the recording track is formed. A detection pattern is provided on that part, integrated with the pit pattern, in order to optically detecting that the light spot of a reading laser beam has moved across the recording track. The method is characterized in that a laser beam is applied at a specific intensity to that part of a photosensitive layer which corresponds to the pit pattern and at a different intensity to the other part of the photosensitive layer, in the process of applying the laser beam to the photosensitive layer to form a latent image corresponding to the detection pattern. The latent image corresponding to the detection pattern is thereby formed to a certain depth in the part corresponding to the pit pattern and to a different depth in the other part of the photosensitive layer.
With the method of manufacturing a master disk, it is possible to easily form an latent image corresponding to a detection pattern, to a particular depth in a part corresponding to a pit pattern and to a different depth in the other part of the photosensitive layer.
According to the invention there is provided a method of manufacturing a master disk for use in manufacturing an optical recording medium that has recording tracks formed along either concentric grooves or a spiral groove. Information is recorded on the lands provided between the grooves. The recording area of the medium has regions where no grooves are made. Each non-groove region has a part corresponding to a land. In this part of each region, a pit pattern representing information about the recording track is formed. A detection pattern is provided on that part, integrated with the pit pattern, in order to optically detect that the light spot of a reading laser beam has moved across the recording track. The method is characterized in that a laser beam is applied with a specific diameter to that part of a photosensitive layer which corresponds to the pit pattern and with a different diameter to the other part of the photosensitive layer, in the process of applying the laser beam to the photosensitive layer to form a latent image corresponding to the detection pattern. The latent image corresponding to the detection pattern is thereby formed to have a certain width in the part corresponding to the pit pattern and a different width in the other part of the photosensitive layer.
With this method of manufacturing a master disk, it is possible to easily form an latent image corresponding to a detection pattern, which has a particular width in a part corresponding to a pit pattern and a different width in the other part of the photosensitive layer.
According to the present invention there is provided a method of accessing tracks provided on the optical recording medium that has recording tracks formed along either concentric grooves or a spiral groove. Information is recorded on the lands provided between the grooves. The recording area of the medium has regions where no grooves are made. Each non-groove region has a part corresponding to a land. In this part of each region, a pit pattern representing information about the recording track is formed. A detection pattern is provided on that part, integrated with the pit pattern, in order to optically detect that the light spot of a reading laser beam has moved across the recording track. The method is characterized in that, in the process of performing a seek operation on the optical recording medium to access a desired recording track, tracks are counted for the regions where no grooves are made, on the basis of the information optically obtained from the detection pattern, and for the regions where grooves are made, on the basis of the information optically obtained from the grooves.
With the method of accessing tracks, it is possible to appropriately access any track on an optical recording medium that has a recording area including regions where no grooves are made.